The subject matter of the present invention is a process for the side-chain chlorination of aromatic compounds which are completely halogenated in the nucleus and contain methyl groups, and have the following general formulas: ##STR2## wherein y=1 or 2, z=0 to 1, x=6-(y+z), n=0 to 8 and k=(8-n), and the methyl groups are in the ortho, meta or para position to one another and in the para position to the oxygen bridge, respectively.
Also subject matter of the invention are 4,4'-bis(chloromethyl)-ar-octahalogendiphenylethers and 4,4'-bis(halogenmethyl)-ar-octahalogendiphenylethers wherein 0.01 to 0.5 Br and 1.5 to 1.99 Cl are divided between the two halogen methyl groups. The compounds are highly brominated in the nucleus and mixtures beginning from Br.sub.6 Cl.sub.2 and extending up to Br.sub.8, and especially those beginning from Br.sub.7 Cl.sub.1, are of especial value.
It is known that methyl aromatics containing chlorine in the nucleus can be successfully chlorinated on the side chain to form technically useful chloromethyl derivatives, but usable processes for the side-chain chlorination of corresponding compounds which are perbrominated in the nucleus are lacking.
If the attempt is made to apply the side-chain chlorination methods commonly used with compounds chlorinated in the nucleus to the analogous methyl aromatics perbrominated in the nucleus, either these methods frequently fail entirely, or, if more severe conditions are applied, a considerable exchange of chlorine for the bromine bound to the nucleus takes place.
Another considerable difficulty arises from the fact that aromatics brominated in the nucleus are prepared as a rule with the use of iron or iron compounds or other metal compounds as catalysts like aluminium chloride. In the large-scale production of these bromine compounds, small amounts of iron always remain in the bromination product, and they can be removed only at considerable expense. But even traces of iron accelerate the exchange of chlorine for bromine in the side-chain chlorination of brominated methyl aromatics, and do so to such an extent that very inconsistent reaction mixtures are obtained which are of scarcely any economical use.